Acid-hardening self-hardening molds are each produced by: adding, to refractory particles such as silica sand, a binder for making foundry molds containing an acid-hardening resin, and a hardener including phosphoric acid, an organic sulfonic acid, sulfuric acid or some other acid; mixing and kneading these components; filling the resultant kneaded sand composition into an original pattern such as a wooden pattern; and then hardening the acid-hardening resin. As the acid-hardening resin, for example, a furan resin, a phenolic resin or the like is used. As the furan resin, for example, the following is used: furfuryl alcohol, furfuryl alcohol/urea-formaldehyde resin, furfuryl alcohol/formaldehyde resin, furfuryl alcohol/phenol/formaldehyde resin, or some other known modified furan resin.
An important requirement for producing a mold is an improvement in the working environment where the mold is produced (when the resin is being hardened). In the case of using, particularly, a furan resin as the acid-hardening resin, it is desired to decrease the amount of formaldehyde generated in the production of the mold. Disclosed is, for example, a method of using a furan-modified urea resin to produce a resin for a self-hardening mold, having excellent storage stability and strength properties without generating much formaldehyde odor (Patent Document 1).
It is disclosed that, for example, 5-hydroxymethylfurfural as an alternative compound to furfuryl alcohol is used as a binder composition which does not substantially contain phenol, formaldehyde nor nitrogen (meaning any amine-containing component such as urea) to decrease harmful substances or gases, thus making it possible to improve the working environment (Patent Document 2).